1. Field of the Invention
The present invention relates generally to the treatment of anatomical tissue of a patient with ultrasound energy and, more particularly, to the ablation of tissue using high intensity focused ultrasound energy.
2. Brief Description of the Related Art
When high intensity ultrasound energy is applied to anatomical tissue, significant physiological effects may be produced in the anatomical tissue resulting from thermal and/or mechanical changes or effects in the tissue. Thermal effects include heating of the anatomical tissue; and, when the tissue is heated to a sufficiently high temperature, tissue damage such as coagulative necrosis is produced. In order to produce thermal effects in anatomical tissue, ultrasound emitting members such as transducers have been used to emit ultrasound energy which is applied to anatomical tissue by positioning the ultrasound emitting members adjacent or in contact with the tissue or by coupling the ultrasound emitting members to the tissue via an acoustic coupling medium, stand-off and/or sheath. By focusing the ultrasound energy at one or more specific focusing zones within the tissue, thermal effect can be confined to a defined location, region, volume or area, and such location, region, volume or area can be remote from the ultrasound emitting member.
With the use of high intensity focused ultrasound (HIFU), one or more focusing zones at or within a designated target location, region, volume or area within a larger mass, body or area of anatomical tissue can be subjected to high intensity ultrasound energy while tissue surrounding the target area is subjected to much lower intensity ultrasound energy. In this manner, tissue in the target area can be heated to a sufficiently high temperature so as to cause a desired thermal effect such as tissue damage, ablation, coagulation, denaturation, destruction or necrosis while tissue surrounding the target area is not heated to damaging temperatures and, therefore, is preserved. Heating of tissue in a target location, volume, region or area to an ablative temperature creates an ablative lesion in the tissue in the target location, volume, region or area that is desirable in the treatment of various medical conditions, disorders or diseases. For example, the lesion may remain as tissue having altered characteristics or may be naturally degraded and absorbed by the patient's body and thusly eliminated such that the remaining body, mass or area of tissue is of smaller volume or size due to the absence of the ablated tissue.
The use of high intensity focused ultrasound to eliminate tissue or to alter the characteristics of tissue in a target location, volume, region or area within a larger mass, body or area of anatomical tissue presents many advantages including minimization of trauma and pain for the patient, elimination of the need for a surgical incision, stitches and exposure of internal tissue, avoidance of damage to tissue other than that which is to be treated, altered or removed, lack of a harmful cumulative effect from the ultrasound energy on the surrounding non-target tissue, reduction in treatment costs, elimination of the need in many cases for general anesthesia, reduction of the risk of infection and other complications, avoidance of blood loss, and the ability for high intensity focused ultrasound procedures to be performed in non-hospital sites and/or on an out-patient basis.
Various devices and/or methods for treating anatomical tissue with ultrasound have been proposed as represented by U.S. Patent Application Publication No. 2005/0080469 to Larson et al. and U.S. Pat. No. 6,858,026 to Sliwa et al., No. 6,840,936 to Sliwa et al., No. 6,805,129 to Pless et al. and No. 6,805,128 to Pless et al., No. 6,413,254 to Hissong et al., No. 6,361,531 to Hissong, No. 6,409,720 to Hissong, No. 6,451,013 to Bays et al., Re. 33,590 to Dory, No. 3,990,452 to Murry et al., No. 4,658,828 to Dory, No. 4,807,633 to Fry, No. 4,858,613 to Fry et al., No. 4,951,653 to Fry et al., No. 4,955,365 to Fry et al., No. 5,033,456 to Pell et al., No. 5,036,855 to Fry et al., No. 5,054,470 to Fry et al., No. 5,065,761 to Pell, No. 5,080,101 to Dory, No. 5,080,102 to Dory, No. 5,117,832 to Sanghvi et al., No. 5,134,988 to Pell et al., No. 5,143,074 to Dory, No. 5,150,711 to Dory, No. 5,150,712 to Dory, No. 5,158,070 to Dory, No. 5,222,501 to Ideker et al, No. 5,267,954 to Nita, No. 5,269,291 to Carter, No. 5,269,297 to Weng et al, No. 5,295,484 to Marcus et al, No. 5,304,115 to Pflueger et al., No. 5,312,328 to Nita et al., No. 5,318,014 to Carter, No. 5,342,292 to Nita et al., No. 5,354,258 to Dory, No. 5,380,274 to Nita, No. 5,391,197 to Burdette et al., No. 5,397,301 to Pflueger et al., No. 5,409,002 to Pell, No. 5,417,672 to Nita et al., No. 5,431,621 to Dory, No. 5,431,663 to Carter, No. 5,447,509 to Mills et al., No. 5,474,530 to Passafaro et al., No. 5,492,126 to Hennige et al., No. 5,501,655 to Rolt et al., No. 5,520,188 to Hennige et al., No. 5,542,917 to Nita et al., No. 5,620,479 to Diederich, No. 5,676,692 to Sanghvi et al., No. 5,728,094 to Edwards, No. 5,730,719 to Edwards, No. 5,733,315 to Burdette et al., No. 5,735,280 to Sherman et al., No. 5,738,114 to Edwards, No. 5,746,224 to Edwards, No. 5,762,066 to Law et al, No. 5,800,379 to Edwards, No. 5,800,429 to Edwards, No. 5,800,482 to Pomeranz et al, No. 5,807,308 to Edwards, No. 5,817,049 to Edwards, No. 5,823,197 to Edwards, No. 5,827,277 to Edwards, No. 5,843,077 to Edwards, No. 5,871,524 to Knowlton, No. 5,873,845 to Cline et al., No. 5,873,902 to Sanghvi et al., No. 5,879,349 to Edwards, No. 5,882,302 to Driscoll, Jr. et al., No. 5,895,356 to Andrus et al, No. 5,928,169 to Schatzle et al. and No. 5,938,608 to Bieger et al.
In particular, the use of high intensity focused ultrasound to thermally damage, ablate, coagulate, denature, cauterize, necrotize or destroy a target volume of tissue is exemplified by U.S. Patent Application Publication No. 2005/0080469 to Larson et al. and U.S. Pat. No. 6,858,026 to Sliwa et al., No. 6,840,936 to Sliwa et al., No. 6,805,129 to Pless et al. and No. 6,805,128 to Pless et al., No. 6,413,254 to Hissong et al., No. 6,361,531 to Hissong, No. 6,409,720 to Hissong, No. 6,451,013 to Bays et al., No. Re. 33,590 to Dory, No. 4,658,828 to Dory, No. 4,807,633 to Fry, No. 4,858,613 to Fry et al., No. 4,951,653 to Fry et al., No. 4,955,365 to Fry et al., No. 5,036,855 to Fry et al., No. 5,054,470 to Fry et al., No. 5,080,101 to Dory, No. 5,080,102 to Dory, No. 5,117,832 to Sanghvi et al., No. 5,143,074 to Dory, No. 5,150,711 to Dory, No. 5,150,712 to Dory, No. 5,295,484 to Marcus et al., No. 5,354,258 to Dory, No. 5,391,197 to Burdette et al., No. 5,431,621 to Dory, No. 5,492,126 to Hennige et al., No. 5,501,655 to Rolt et al., No. 5,520,188 to Hennige et al, No. 5,676,692 to Sanghvi et al, No. 5,733,315 to Burdette et al, No. 5,762,066 to Law et al., No. 5,871,524 to Knowlton, No. 5,873,845 to Cline et al, No. 5,873,902 to Sanghvi et al., No. 5,882,302 to Driscoll, Jr. et al., No. 5,895,356 to Andrus et al., No. 5,928,169; to Schätzle et al, and No. 5,938,608 to Bieger et al.
Heart arrhythmias, such as atrial fibrillation, have been treated by surgery. For example, a surgical procedure called the “Maze” procedure was designed to eliminate atrial fibrillation permanently. The procedure employs incisions in the right and left atria which divide the atria into electrically isolated portions which in turn results in an orderly passage of the depolarization wave front from the sino-atrial node (SA Node) to the atrial-ventricular node (AV Node) while preventing reentrant wave front propagation. Although successful in treating AF, the surgical Maze procedure is quite complex and is currently performed by a limited number of highly skilled cardiac surgeons in conjunction with other open-heart procedures. As a result of the complexities of the surgical procedure, there has been an increased level of interest in procedures employing ultrasound devices or other types of ablation devices, e.g. thermal ablation, micro-wave ablation, RF ablation, cryo-ablation or the like to ablate tissue along pathways approximating the incisions of the Maze procedure. Electrosurgical systems for performing such procedures are described in U.S. Pat. No. 5,916,213 to Haissaguerre, et al., U.S. Pat. No. 5,957,961 to Maguire, et al. and U.S. Pat. No. 5,690,661, all incorporated herein by reference in their entireties. Procedures are also disclosed in U.S. Pat. No. 5,895,417 to Pomeranz, et al, U.S. Pat. No. 5,575,766 to Swartz, et al., U.S. Pat. No. 6,032,077 to Pomeranz, U.S. Pat. No. 6,142,994 to Swanson, et al. and U.S. Pat. No. 5,871,523 to Fleischman, et al., all incorporated herein by reference in their entireties. Cryo-ablation systems for performing such procedures are described in U.S. Pat. No. 5,733,280 to Avitall, also incorporated herein by reference in its entirety. High intensity focused ultrasound systems for performing such procedures are described in U.S. Patent Application Publication No. 2005/0080469 to Larson et al. and U.S. Pat. No. 6,858,026 to Sliwa et al., No. 6,840,936 to Sliwa et al., No. 6,805,129 to Pless et al. and No. 6,805,128 to Pless et al., all incorporated herein by reference in their entireties.
High intensity focused ultrasound is an attractive surgical ablation modality as the energy can be focused to create heat at some distance from the transducer. In epicardial applications, most of the heat loss is to the blood, which is also some distance from the transducer. This is in contrast to most other technologies, in which heating occurs close to the transducer (or electrode) and deeper heating is by thermal conduction. Additionally, since the coronary arteries are typically towards the epicardial surface, they are theoretically less susceptible to heating and subsequent constriction by a device such as a HIFU device, which can generate heat deep within the myocardium. For example, a non-irrigated RF epicardial ablation approaches has the highest heating occurring at the epicardial surface. Any transfer of heat to the deeper endocardium is by thermal conduction. Irrigated RF epicardial ablation approaches allow the heat to penetrate deeper into the tissue, but are nonetheless limited in depth. In contrast, a HIFU approach can focus the energy to generate heat deeper within the tissue at a substantial distance from the transducer.
Another therapeutic method to terminate AF is to ablate an area that is sufficiently large enough such that there is not enough critical mass to sustain the reentrant waveform characteristic of the arrhythmia.
In conjunction with the use of ablation devices, various control mechanisms have been developed to control delivery of ablation energy to achieve the desired result of ablation, i.e. killing of cells at the ablation site while leaving the basic structure of the organ to be ablated intact. Such control systems may include measurement of temperature and/or impedance at or adjacent to the ablation site, as are disclosed in U.S. Pat. No. 5,540,681 to Struhl, et al., incorporated herein by reference in its entirety.
Additionally, there has been substantial work done toward assuring that the ablation procedure is complete, i.e. that the ablation extends through the thickness of the tissue to be ablated, before terminating application of ablation energy. This desired result is some times referred to as a “transmural” ablation. For example, detection of a desired drop in electrical impedance at the electrode site as an indicator of transmurality is disclosed in U.S. Pat. No. 5,562,721 to Marchlinski et al., incorporated herein by reference in its entirety. Alternatively, detection of an impedance rise or an impedance rise following an impedance fall are disclosed in U.S. Pat. No. 5,558,671 to Yates and U.S. Pat. No. 5,540,684 to Hassler, respectively, also incorporated herein by reference in their entireties.
Three basic approaches have been employed to create elongated lesions using ablation devices. The first approach is simply to create a series of short lesions using a contact electrode, moving it along the surface of the organ wall to be ablated to create a linear lesion. This can be accomplished either by making a series of lesions, moving the electrode between lesions or by dragging the electrode along the surface of the organ to be ablated and continuously applying ablation energy, as described in U.S. Pat. No. 5,897,533 to Mulier, et al., incorporated herein by reference in its entirety. The second basic approach to creation of elongated lesions is simply to employ an elongated electrode, and to place the elongated electrode along the desired line of lesion along the tissue. This approach is described in U.S. Pat. No. 5,916,213, cited above. The third basic approach to creation of elongated lesions is to provide a series of electrodes and arrange the series of electrodes along the desired line of lesion. The electrodes may be activated individually or in sequence, as disclosed in U.S. Pat. No. 5,957,961, also cited above. In the case of multi-electrode devices, individual feedback regulation of ablated energy applied via the electrodes may also be employed.